What do humans and seed have in common? 

Actually, quite a bit.  When you breathe, you inhale air (21% oxygen) and exhale carbon dioxide in a process called respiration.  When a seed breathes, it also inhales air (21% oxygen) and exhales carbon dioxide, the same process…respiration.  Respiration is used to break down stored carbon (food) into usable energy, and oxygen drives the process.

Seed Shelf Life

As most people involved with seed know, the shelf life of a seed is highly dependent on the environmental condition in which that seed is stored.  Common knowledge says that most dry seed stored in cool, dry conditions will survive longer than a seed stored in a wet, warm environment.

Why cool and dry is the best.

The amount of moisture in the seed determines which chemical reactions are most likely to occur in that seed.  Some reactions are good for the seed….and some are not so good.

When seed is dried to storable moisture levels (5% to 12% depending on the species), things are still happening inside that seed sitting on the shelf, but they are happening very, very slowly, mostly due to the lack of seed moisture.  The chemical reactions that do occur at these low moisture levels are generally bad for the seed, wasting seed energy and creating products that are not needed for good healthy seed germination.  So…slowing down these reactions as much as possible is key.  Lower seed moisture levels are the most important way, but a cool environment also slows everything down.  The picture shows Manny Govea heat-sealing a bag of seed to keep out moisture.  Some companies have even placed dehydration bags inside the seed package as further protection against moisture.  People have also tried to either vacuum seal the seed package to reduce the amount of oxygen inside, insert oxygen-absorbing cachets into the seed package or inject an inert gas such as nitrogen into the seed packet, which evacuates the oxygen.  All three of these are thought to slow chemical reactions in the seed by reducing oxygen, the driving force behind these reactions.  However, the research on the benefits of low oxygen seed storage is not conclusive.

As seed moisture increases from 5%-12% to around 20-30%, the speed of these bad chemical reactions increase dramatically, and so does seed deterioration.  At around 30% to 45% seed moisture, seed germination processes are initiated and, if other factors are favorable, seed germination can occur.  This is also the moisture level where most seed is primed (see article #4 in this series).  Increasing seed moisture further, results in too much water, and a different set of reactions taking place, which are generally not good for seed health.

Next time we’ll talk about “Seed Conditioning – Separating the Good Seed from the Bad”, and not only some of the common ways, but also the new technologies.  See you then.

Keith